Apparatuses for collecting and removing solid particles from a flowing fluid are commonly known. They are used in sewage treatment plants in which domestic or industrial sewage is cleaned. They are also used to clean washing water or process water or to screen mud or the like.
An apparatus for collecting and removing solid particles from a flowing fluid is known from European Patent No. EP 0 221 991 B1. The apparatus includes a first set of stationary bars and a second set of movable bars. The stationary bars and the movable bars are alternately arranged, and they include steps at their side facing the flowing fluid. The steps include a substantially horizontal skeleton portion and a substantially vertical rising portion in a way that the steps form a rectangular stepped curve. The movable bars are interconnected to form a movable bar unit being suspended at and connected to two eccentric discs. The first eccentric disc is directly connected to the movable bar unit. The second eccentric disc uses a rod to transmit the movement onto the movable bar unit. The two eccentric discs are coupled, and each of them forms a drive. In this way, the movable bar unit is guided along a closed circular path with respect to the stationary bars in a forced manner. The movable bar unit is guided along one single circular path at all of its locations. The upwardly directed component of movement of the circular path is slightly greater than the height of the steps of the stationary bars. The movable bars together with side walls form a unit. The side walls are used to transmit the circular movement onto the bars. The suspension of the movable bar unit is rather complicated, and it requires a separation of the drive via two separate eccentric discs and the corresponding suspension at two places.
Another separating similar grid is known from European Patent No. EP 0 682 551 B1. The separating grid includes a stationary bar unit and a movable bar unit. A driving mechanism is arranged above the flowing fluid to move the movable bar unit along a closed and substantially circular path of movement. The movement includes a vertical component of movement which is greater than the height of the steps of the bars. The drive for the movable bar unit is designed such that the movable bar unit in its upper region is exactly guided on a circular path. The circular movement is provided by an eccentric device. The drive also includes a pulling element with a connecting mechanism providing a path of movement being similar to a circuit. In this way, the movable bar unit at each point is differently moved about the height of the bars. Each step is moved on a different path of movement. The path of movement is closed, and it is very similar to a circuit. The circuit includes a vertical component of movement the value of which is greater than the height of the steps of the bars. With this arrangement, the solid particles are not correctly transported in an upward direction. The conveying effect is different at all steps.
A step screen is known from German Patent Application No. DE 197 14 089 A1. The step screen includes a first bar unit including stationary and spaced apart bars and a second bar unit including movable bars. All bars include a majority of steps at their surface facing the flowing fluid. The steps include a horizontal skeleton portion and a vertical rising portion. The movable second bar unit is driven along a closed path of movement in the plane of main extension of the bars. The upwardly directed component of movement of the path of movement is slightly greater than the vertical height of the steps of the bars. The drive includes two separately controllable actuating drives driving the movable bar unit in two different actuating directions. In this way, the adjustment of the movable bar unit is more variable. The path of movement surrounds a surface, and it is divided into substantially linear sections of the movement, the sections preferably being vertical and linear. The actuating drives are arranged to be vertical and horizontal. Consequently, the circular movement known from the above described prior art is replaced by a rectangular movement.